Chemical-mechanical-polishing system with continuous filtration

ABSTRACT

A chemical-mechanical-polishing system having a slurry distribution system, a polisher, a deionized water supply, and a drain, includes a slurry filtration system. The filtration system has two filters for alternately filtering particles in slurry and being backflushed with deionized water. Two input valves have input ports connected to the slurry distribution system and output ports respectively connected to the filters for filtering. Two output valves have input ports respectively connected to the filters for receiving filtered slurry and output ports connected to the polisher. Two backflush valves have input ports connected to the deionized water supply and output ports respectively connected to backflush with deionized water; the output ports are also respectively connected to the input ports of the two output valves. Two drain valves have input ports respectively connected to the filters for receiving backflushed fluid and output ports connected to the drain. A pressure sensor disposed to sense pressure of slurry across the filters provide pressure indications which are used by control circuitry to open and close said valves to filter slurry or backflush the filters.

TECHNICAL FIELD

The present invention relates generally to chemical-mechanical-polishingsystems for processing semiconductors and more specifically tochemical-mechanical-polishing systems which include filtration systems.

BACKGROUND ART

In the past, a chemical-mechanical polishing (CMP) process was developedfor planarization of semiconductor surfaces and metal inlays duringmanufacturing. A chemical, a base or neutral for semiconductor oxidesurfaces and an acid for metals, with a number of other proprietarychemicals would be used to soften the surface material and an abrasive,such as alumina or silicon, would be used for planarization in a machinecalled a polisher. The chemicals have a pH range of 2 to 11 and carrythe abrasive in suspension as a slurry which is kept constantly inmotion to prevent separation.

As semiconductor devices were reduced in size, it became desirable touse CMP processing to obtain increasingly flat surfaces. As CMP came tobe used in semiconductors with line geometries of 0.35 micron, it becamecommon to provide filtration systems to control the size of particlesreaching the polisher in order to reduce the defects caused by particlescratches. Smaller particles cause smaller scratches but with smallerline geometries, the smaller scratches still negatively affect the finalsemiconductor device. With sub-0.35 micron semiconductor devices,filtration systems are universally used either as part of therecirculating system for the slurry or directly in the line to thepolisher.

The problem with current filtration systems is that they must compromisebetween the particle size that can be filtered out and the time betweenreplacement of the filter. For example, the smaller the particle sizefiltered, the sooner the filter must be replaced. This filterreplacement interrupts production for a significant amount of time andreduces the number of semiconductor devices which can be produced.Conversely, allowing larger particles to the polisher for longer filterlife results in increased defects which also reduces the number ofsemiconductor devices which can be produced even though production cancontinue longer without interruption.

A solution, which would allow continuous filtration of small particles,has long been sought, but has also long eluded those skilled in the art.Such a solution would be highly valuable since the economics ofsemiconductor production equate small improvements in production tolarge sums of money because of the high selling price of semiconductordevices.

DISCLOSURE OF THE INVENTION

The present invention provides processing apparatus which includes afiltration system having dual filters, a valve system, pressure sensing,and controls for controlling filtering, backflushing, and precharging.The control system switches the valve system to filter in one filterwhile backflushing in the other. After backflushing the other filter, itis precharged with filtered fluid before the one filter is backflushedand the other begins filtering.

An advantage of the present invention is to provide a system whichpermits continuous filtration of large particles and cleaning offilters.

Another advantage of the present invention is to provide a system whichautomatically permits continuous filtration of large particles andcleaning of filters.

Another advantage of the present invention is to provide a filtrationsystem in which the filters never need replacement.

Another advantage of the present invention is to provide a CMP system inwhich the filtration system can continuously filter the slurry andautomatically change filters.

Another advantage of the present invention is to provide a CMP system inwhich the filtration system can continuously filter the slurry, cleanthe filters, and automatically change filters when required.

The above and additional advantages of the present invention will becomeapparent to those skilled in the art from a reading of the followingdetailed description when taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a CMP system with a recirculating CMP filtration systemfiltering through a first filter and backflushing a second filter;

FIG. 2 is a CMP system with a recirculating CMP filtration systemfiltering through the second filter and backflushing the first filter;

FIG. 3 is a CMP system with an in-line CMP filtration system filteringthrough the first filter with the backflushing of the second filterstopped;

FIG. 4 is a CMP system with an in-line CMP filtration system filteringthrough the first filter and precharging the second filter; and

FIG. 5 is a CMP system with a simplified in-line CMP filtration systemfiltering through the first filter and backflushing the second filter.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, therein is shown a chemical-mechanicalpolishing (CMP) system 10 which uses a particulate-containing fluid,called "slurry", for flattening oxide and metal surfaces ofsemiconductors. The CMP system 10 consists of a slurry distributionsystem 12, a CMP filtration system 14 in the recirculation line of theslurry distribution system 12, and a polisher 16. Also connected to theCMP system 10 is a source of deionized water 18 and a drain 20.

The CMP filtration system 14 includes first and second input solenoidvalves 22 and 24, respectively. Each of the first and second inputvalves 22 and 24 have their input ports connected to the slurrydistribution system 12 and their output ports respectively connected tofirst and second filters 26 and 28, respectively.

The first and second filters 26 and 28 can be single or multistagefilters which are filter particles that are sized as a function of theline geometries of the semiconductor devices which are being polished.For example, in a 0.18 micron line geometry semiconductor device, thefilters 26 and 28 would filter out particles over 10 nanometers in sizein slurry flowing in a first direction through the filters. The filters26 and 28 are backflushed by flowing deionized water through the filtersin a second direction, which is the opposite of the first direction.

The first and second filters 26 and 28 are respectively connected tofirst and second output solenoid valves 30 and 32. Each of the first andsecond output valves 30 and 32 have their input ports respectivelyconnected to said first and second filters 26 and 28, and their outputports connected to the polisher 16.

A pressure sensor 34 is located on the connection between the first andsecond output valves 30 and 34 and the polisher 16. The pressure sensor34 senses the fluid pressure out of the first or second filter 26 or 28and gives an indication thereof to cause the filtering filter to beautomatically switched when it is filled to the point where a cleanfiller should be filtering.

It should be noted that one pressure sensor 34 is sufficient if thecontrol system 48 is connected to the pump 38 to tell if it is running.If the CMP filtration system 14 is electrically isolated from the pump38, an additional pressure sensor would be required at the input to thefirst and second input valves 22 and 24 to provide an indication of thepressure drop across the first and second filters 26 and 28. The controlsystem would automatically shift the filtration between filters when onewas filled up. Different arrangements of pressure sensors, for exampleacross each filter, would be evident to those skilled in the art basedon how desirable it is to have various fail-safe arrangements.

Between the pressure sensor 34 and the polisher 16 for the recirculatingCMP filtration system 14 is the recirculating connection back to aslurry reservoir 36 in the slurry distribution system 12. The slurrydistribution system 12 contains a recirculation pump 38 which causes theslurry to flow through the CMP system 10 to the polisher 16.

Also shown in FIG. 1 connected to the deionized water supply 18 arefirst and second backflush solenoid valves 40 and 42. Each of the firstand second backflush valves 40 and 42 have input ports connected to thedeionized water supply 18 and output ports, respectively, connected tothe first and second filters 26 and 28 for backflushing by flowingdeionized water therethrough in said second direction. The output portsof the first and second backflush valves 40 and 42 are also respectivelyconnected to the inputs of the first and second output valves 30 and 32in order to respectively connect the valves to the second and firstfilters 28 and 26.

The first and second filters 26 and 28 are connected to first and seconddrain solenoid valves 44 and 46. Each of the drain valves 44 and 46 haveinput ports respectively connected to the first and second filters 26and 28 for receiving backflushed deionized water flow through thefilters in said second direction, and output ports connected to thedrain 20. The output ports of the first and second drain valves 44 and46 are also connected to the outputs of the first and second inputvalves 22 and 24 in order to respectively connect the valves to thesecond and first filters 28 and 26.

Also shown in FIG. 1 is control circuitry 48 for responding to thepressure sensor 34 to activate the various solenoid valves in variouscombinations as will later be explained. The control circuitry 48 couldbe a simple adjustable electrical timer based system but in the bestmode is a fully controllable microprocessor based system.

FIG. 1 shows the CMP system 10 with the CMP filtration system 14 in anoperational mode in which the first filter 26 is filtering and thesecond filter 28 is being backflushed.

Referring now to FIG. 2, therein is shown the CMP system 10 with the CMPfiltration system 14 in a second operational mode in which the firstfilter 26 is being backflushed and the second filter 28 is filtering.

Referring now to FIG. 3, therein is shown a CMP system 50 with the CMPfiltration system 14 in-line between a recirculating slurry distributionsystem 52 and the polisher 16. The CMP filtration system 14 is shown inanother operational mode in which the first filter 26 is filtering andthe backflushing of the second filter 28 is stopped.

Referring now to FIG. 4, therein is shown a CMP system 50 with the CMPfiltration system 14 in-line between a recirculating slurry distributionsystem 52 and the polisher 16. The CMP filtration system 14 is shown inanother operational mode in which the first filter 26 is filtering andthe second filter 28 is being precharged with slurry and is connected tothe drain 20 to force the deionized water from the second filter 28before restarting filtering.

Referring now to FIG. 5, therein is shown a CMP system 60 with asimplified CMP filtration system 64 in-line between the recirculatingslurry distribution system 52 and the polisher 16. The common elementsherein are given the same numbers as in previous FIG's. A four-way,two-position, input solenoid valve 62 has: a first port connected to therecirculating slurry distribution system 52; a second port to the drain20; a third port to the first filter 26; and a fourth port to the secondfilter 28. A four-way, two-position, output solenoid valve 66 has: afirst port to the first filter 26; and a second port to the secondfilter 28; a third port connected to the polisher 16; and a fourth portto the deionized water supply 18. The solenoids are controlled by asimple adjustable timer control system 68.

In operation in a first mode, as shown in FIG. 1 for filtering in thefirst filter 26, the slurry distribution system 12 has the pump 38pumping slurry from the slurry reservoir 36 to the first and secondinput valves 22 and 24 along the direction indicated by the dottedarrows. The positions of the various solenoid valves are set by thecontrol system 48.

The slurry is a suspension of an abrasive, such as alumina or silicon,carried generally by a neutral pH chemical or base, such as ammoniumhydroxide or potassium hydroxide, for polishing semiconductor oxidesurfaces and an acid, such as ferric nitrate or potassium iodate orhydrogen peroxide, for polishing metals. The slurry also contains anumber of other proprietary chemicals which assist in CMP. The slurry isin a pH range of 2 to 11. Some slurries are so unstable that theabrasives tend to clump or fall out of suspension in a few hours. Theslurry is kept constantly in motion to prevent separation as much aspossible.

As shown in FIG. 1, the first and second input valves 22 and 24 are inthe positions in which the first input valve 22 is open to allow theflow of slurry through to the first filter 26 while the second inputvalve 24 is off to prevent flow. The first filter 26 filters outparticles larger than the optimum for the CMP polisher 16 based on theline geometries of the semiconductor device being polished.

The filtered slurry then flows to the first output valve 30 which isopen to permit the slurry to flow past the pressure sensor 34 to thepolisher 16. As shown, the second output valve 32 is closed. Thepressure sensor 34 measures the pressure of the slurry after it passesthrough either the first filter 26 or the second filter 28. It isconnected to the control system 48 and provides an indication when afilter is filled up with enough abrasive particles to warrant switchingto the other filter and backflushing.

After flowing through the CMP filtration system 14 and past the pressuresensor 34, the slurry is also partially redirected back to the slurrydistribution system 12 for recirculation before flowing on to thepolisher 16 where it is used up in the CMP process.

While the slurry is being filtered in the first filter 26, the deionizedwater supply 18 provides deionized water along the direction of thesolid arrows to the first and second backflush valves 40 and 42. Thedeionized water may contain a buffering chemical because some slurriesare extremely sensitive to changes in pH. Changes in pH which "shock"the slurry will cause the abrasive to clump together into larger sizeparticles or will cause the particles to come out of suspension. Thus,the buffering chemical will prevent shocking the slurry when itencounters deionized water in a previously backflushed filter.

The first backflush valve 40 is closed but the second backflush valve 42is open to allow deionized water to flow to backflush the second filter28. The backflushed fluid carries the large size particles from thesecond filter 28 to the second input valve 24 which is closed andthrough the second drain valve 46 which is open. From the second drainvalve 46, the backflushed fluid flows to the drain 20. It should beunderstood that the drain 20 may be a reclamation system or furtherprocessing system rather than just a plain drain.

In operation in a second mode, as shown in FIG. 2 for filtering in thesecond filter 28, the slurry distribution system 12 has the pump 38pumping slurry from the slurry reservoir 36 to the first and secondinput valves 22 and 24 along the direction indicated by the dottedarrows. The positions of the various solenoid valves are set by thecontrol system 48.

As shown in FIG. 2, the first and second input valves 22 and 24 are inthe positions in which the first input valve 22 is off to prevent flowwhile the second input valve 24 is open to allow the flow of slurrythrough to the second filter 28. The second filter 28 filters outparticles larger than the optimum for the CMP polisher 16 based on theline geometries of the semiconductor device being polished. The filteredslurry then flows to the second output valve 32 which is open to permitthe slurry to flow past the pressure sensor 34 to the polisher 16. Asshown, the first output valve 30 is closed. Once past the pressuresensor 34, which measures the pressure drop of the fluid through the CMPfiltration system 14 and indicates the degree to which the filteringfilter is filled up, the slurry is also partially redirected to theslurry distribution system 12 for re-circulation.

While the slurry is being filtered in the second filter 28, thedeionized water supply 18 provides deionized water, which may include abuffering chemical, along the direction of the solid arrows to the firstand second backflush valves 40 and 42. The first backflush valve 40 isopen to allow deionized water to flow to backflush the first filter 26but the second backflush valve 42 is closed. The backflushed fluid fromthe first filter 26 flows to the first input valve 22 which is closedand through the first drain valve 44 which is open. From the first drainvalve 44, the backflushed fluid flows to the drain 20.

In operation, as shown in FIG. 3 for filtering in the first filter 26and stopping backflushing to conserve deionized water, the slurrydistribution system 12 has the pump 38 pumping slurry from the slurryreservoir 36 to the first and second input valves 22 and 24 along thedirection indicated by the dotted arrows. The positions of the varioussolenoid valves are set by the control system 48.

As shown in FIG. 3, the first and second input valves 22 and 24 are inthe positions in which the first input valve 22 is open to allow theflow of slurry through to the first filter 26 while the second inputvalve 24 is off to prevent flow. The first filter 26 filters outparticles larger than the optimum for the CMP polisher 16 based on theline geometries of the semiconductor device being polished.

The filtered slurry then flows to the first output valve 30 which isopen to permit the slurry to flow past the pressure sensor 34 to thepolisher 16. As shown, the second output valve 32 is closed. Thepressure sensor 34, which measures the pressure drop of the fluidthrough the CMP filtration system 14, indicates the degree to which thefiltering filter is filled up.

While the slurry is being filtered in the first filter 26, the deionizedwater supply 18 stops providing deionized water because the controlsystem 48 causes the first and second backflush valves 40 and 42 to beclosed.

In operation, as shown in FIG. 4 for filtering in the first filter 26and precharging the second filter 28, the slurry distribution system 12has the pump 38 pumping slurry from the slurry reservoir 36 to the firstand second input valves 22 and 24 along the direction indicated by thedotted arrows. The positions of the various solenoid valves are set bythe control system 48.

After backflushing a filter, it is desirable to "precharge" the filterby sending slurry through it because the residual deionized water whichis used in the backflushing can shock the slurry and cause the abrasiveto fall out of suspension.

A "precharging" mode is shown in FIG. 4. The slurry from the firstoutput valve 30 would have a portion diverted to the second output valve32 which would be open. The first and second backflush valves 40 and 42would be closed, the second input valve 24 would be closed, and thesecond drain valve 46 would be open. In this mode, the slurry would flowfrom the second output valve 32 back through the second filter 28 to thesecond drain valve 46 and to the drain 20, and the residual deionizedwater flows through the open second drain valve 46 into the drain 20.Since the large size particles would be filtered out by the first filter26, the reverse flow of slurry through the second filter 28 would notfill it up.

After precharging, the second drain valve 46 would be closed and thecontrol system 48 would set the solenoid valves in the CMP filtrationsystem 14 to filter through the second filter 28 and backflush the firstfilter 26.

In operation, as shown in FIG. 5 for filtering in the first filter 26,the slurry distribution system 52 has the pump 38 pumping slurry fromthe slurry reservoir 36 to the input valve 62 along the directionindicated by the dotted arrows. The positions of the two solenoid valves62 and 66 are set by the adjustable timer control system 68.

As shown in FIG. 5, the input valve 62 is in a first position in whichthe flow of slurry is through to the first filter 26. From the firstfilter 26, the slurry flows to the output valve 66 which is also in thefirst position which directs the flow to the polisher 16. With thevalves 62 and 66 in their first positions, the deionized water supply isconnected through the output valve 66 to backflush the second filter 28.The backflushed fluid from the second filter 28 then flows through theinput valve 62 to the drain 20.

When the adjustable time control system 68 is set based on the expectedservice time to filter fillup, it will switch the valves 62 and 66 totheir second positions. In the second positions, the slurry is pumpedthrough the input valve 62 to the second filter 28 and then through theoutput valve 64 to the polisher 16. At the same time, the deionizedwater will flow through the output valve 66 to backflush the firstfilter 26. The deionized water carrying the particulates from the firstfilter 26 will exit through the input valve 62 to the drain 20.

As would be evident to those skilled in the art, while the best modeshave been described using separate commercially available solenoidvalves, a single custom solenoid valve with appropriate internal valveparts could accomplish all the functions described herein. For example,a single four-position, four-way valve could provide all four modes ofoperation.

While the invention has been described in conjunction with a specificbest mode, it is to be understood that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations which fall within thespirit and scope of the appended claims. All matters set forth herein orshown in the accompanying drawings are to be interpreted in anillustrative and non-limiting sense.

The invention claimed is:
 1. Apparatus comprising:a source ofparticulate containing fluid; a user of particulate containing fluid; asource of backflushing fluid; a drain for said fluids; a first filter; asecond filter; valving means for respectively connecting in first andsecond modes:said source of particulate containing fluid through saidfirst filter to said user of said particulate containing fluid and saidsource of backflushing fluid through said second filter to said drainfor said fluids; and said source of particulate containing fluid throughsaid second filter to said user of said particulate containing fluid andsaid source of backflushing fluid through said first filter to saiddrain for said fluids; said valving means includes precharging valvingmeans for connecting said source of particulate containing fluid to saidfirst filter during said second mode and said second filter during saidfirst mode; and a control system for changing said valving means betweensaid first and second modes.
 2. Apparatus as claimed in claim 1including pressure sensing means for sensing fluid pressure at saidfirst and second filters and providing an indication thereof to saidcontrol system, and wherein said control system includes means forcausing said valving means to shift between said first and second modesin response to predetermined indications of said fluid pressure at saidfirst and second filters.
 3. Apparatus as claimed in claim 1 includingpressure sensing means for sensing the pressure drop across said firstand second filters and providing an indication thereof to said controlsystem, and wherein said control system includes means for causing saidvalving means to shift between said first and second modes in responseto said indication of the pressure drop across said first and secondfilters.
 4. Apparatus as claimed in claim 1 wherein said valving meansincludes backflush valving means for respectively isolating said sourceof backflushing fluid from said first and second filters during saidfirst and second modes.
 5. Apparatus as claimed in claim 1 wherein saidvalving means includes drain valving means for connecting said drain tosaid first filter during said second mode and to said second filterduring said first mode.
 6. Apparatus as claimed in claim 1 whereincontrol system includes means for causing said valving means to: connectsaid source of particulate containing fluid alternately through saidfirst and second filters to said user of particulate containing fluid;connect said source of particulate containing fluid to both said firstand second filters; and connect said first and second filtersindividually to said drain for said fluids.
 7. Apparatus as claimed inclaim 1 wherein control system includes means for causing said valvingmeans to: connect said source of particulate containing fluidalternately through said first and second filters to said user ofparticulate containing fluid; connect said source of particulatecontaining fluid to both said first and second filters; connect saidsource of backflushing fluid alternatively through said first and secondfilters to said drain for said fluids; and connect said first and secondfilters individually to said drain for said fluids.
 8. Apparatus asclaimed in claim 1 wherein said source of particulate containing fluidprovides for circulation of a portion of said particulate containingfluid to said user of said particulate containing fluid through saidfirst filter in said first mode and through said second filter in saidsecond mode and back to said source of particulate containing fluid. 9.Apparatus as claimed in claim 1 wherein said source of particulatecontaining fluid provides for circulation of a portion of saidparticulate containing fluid therein and the remainder to said user ofparticulate containing fluid through said first filter in said firstmode and through said second filter in said second mode.